Attachment_0004_UFC_3_450_01.pdf

UFC 3-450-01

15 May 2003

UNIFIED FACILITIES CRITERIA (UFC)

NOISE AND VIBRATION CONTROL

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

UNIFIED FACILITIES CRITERIA (UFC)

NOISE AND VIBRATION CONTROL

Any copyrighted material included in this UFC is identified at its point of use.

Use of the copyrighted material apart from this UFC must have the permission of the copyright holder.

U.S. ARMY CORPS OF ENGINEERS (Preparing Activity)

NAVAL FACILITIES ENGINEERING COMMAND

AIR FORCE CIVIL ENGINEER SUPPORT AGENCY

Record of Changes (changes are indicated by \1\ ... /1/)

Change No. Date Location

This UFC supersedes TM 5-805-4, dated 26 May 1995. The format of this UFC does not conform to UFC 1-300-01; however, the format will be adjusted to conform at the next revision. The body of this UFC is a document of a different number.

FOREWORD

\1\ The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance with USD(AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and work for other customers where appropriate. All construction outside of the United States is also governed by Status of forces Agreements (SOFA), Host Nation Funded Construction Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)

Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the SOFA, the HNFA, and the BIA, as applicable.

UFC are living documents and will be periodically reviewed, updated, and made available to users as part of the Services’ responsibility for providing technical criteria for military construction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities Engineering Command (NAVFAC), and Air Force Civil Engineer Support Agency (AFCESA) are responsible for administration of the UFC system. Defense agencies should contact the preparing service for document interpretation and improvements. Technical content of UFC is the responsibility of the cognizant DoD working group. Recommended changes with supporting rationale should be sent to the respective service proponent office by the following electronic form: Criteria Change Request (CCR). The form is also accessible from the Internet sites listed below.

UFC are effective upon issuance and are distributed only in electronic media from the following source:

• Whole Building Design Guide web site http://dod.wbdg.org/.

Hard copies of UFC printed from electronic media should be checked against the current electronic version prior to use to ensure that they are current.

AUTHORIZED BY:

DONALD L. BASHAM, P.E.

Chief, Engineering and Construction U.S. Army Corps of Engineers

DR. JAMES W WRIGHT, P.E.

Chief Engineer Naval Facilities Engineering Command

KATHLEEN I. FERGUSON, P.E.

The Deputy Civil Engineer DCS/Installations & Logistics Department of the Air Force

Dr. GET W. MOY, P.E.

Director, Installations Requirements and Management Office of the Deputy Under Secretary of Defense (Installations and Environment) http://www.wbdg.org/pdfs/ufc_implementation.pdf http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4 http://dod.wbdg.org/

ARMY TM 5-805-4

AIRFORCE AFJMAN 32-1090

TECHNICAL MANUAL

NOISE AND VIBRATION CONTROL

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION IS UNLIMITED

HEADQUARTERS, DEPARTMENTS OF THE ARMY AND THE AIR FORCE

26 26 MAY 19951995

REPRODUCTION AUTHORIZATION/RESTRICTIONS

This manual has been prepared by or for the Government and, except to the extent indicated below, is public property and not subject to copyright.

Copyrighted material included in the manual has been used with the knowledge and permission of the proprietors and is acknowledged as such at point of use. Anyone wishing to make further use of any copyrighted material, by itself and apart from this text, should seek necessary permission directly from the proprietors.

Reprints or republications of this manual should include a credit substantially as follows: “Joint Departments of the Army and Air Force, TM 5-8054/AFJMAN 32-1090 Noise and Vibration Control

If the reprint or publication includes copyrighted material, the credit should also state: “Anyone wishing to make further use of copy-righted material, by itself and apart from this text, should seek necessary permission directly from the proprietors.”

A

*TM 5-805-4/AFJMAN 32-1090

TECHNICAL MANUAL HEADQUARTERS

NO. 5-805-4 DEPARTMENTS OF THE ARMY

AIR FORCE MANUAL AND THE AIR FORCE

NO. 88-37 WASHINGTON, DC, 26 May 1995

NOISE AND VIBRATION CONTROL

Paragraph Page

CHAPTER 1. GENERAL

Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1-1 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-1 Noise Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 1-1 English, Metric Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5 1-1 Explanation of Abbreviation and Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6 1-1

2. Noise and Vibration Criteria General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2-1 Noise Criteria In Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2-1 Vibration Criteria In Building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 2-4

3. Sound Distribution Indoors General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3-1 Sound Pressure Level in a Room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3-1 Room Constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3 3-2 Sample Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4 3-4

4. Sound Isolation Between Rooms Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4-1 Sound Transmission Loss (TL), Noise Reduction (NR) & Sound Transmission Class (STC) 4-2 4-1 Transmission Loss-Walls, Doors, Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 4-4 Transmission Loss of Floor-Ceiling Combinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4 4-6

5. Sound Propagation Outdoors Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5-1 Distance Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 5-1 Atmospheric Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5-4 Terrain and Vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4 5-6 Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5 5-7 Reception of Outdoor Noise Indoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5-11 Combined Effects, Sample Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7 5-12 Source Directivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8 5-13

6. Airborne Sound Control Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6-1 Indoor Sound Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 6-1 Outdoor Sound Problem and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 6-2 Quality of Analysis Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4 6-2 Noise Control Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6-3

7. Air Distribution Noise for Heating, Ventilating and Air Conditioning SYSTEMS Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7-1 General Spectrum Characteristics of Noise Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2 7-1 Specific Characteristics of Noise Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3 7-1 Control of Fan Noise in a Duct Distribution System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4 7-3 Procedure for Calculating Noise Control Requirements for an Air Distribution System . . . . 7-5 7-7 Calculation Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 7-9

8. Vibration Control Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8-1 Vibration Isolation Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 8-1 Mounting Assembly Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3 8-3 Tables of Recommended Vibration Isolation Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4 8-6 Vibration Isolation-Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5 8-10

9. Mechanical Noise Specifications Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 9-1 General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2 9-1

This manual supersedes TM 5-805-4/AFM 88-37/NAVFAC DM 3.10, dated 30 December 1983, recind DD Forms 2294, 2295, 2296, 2297, 2298, 2299, 2300, 2301, 2302, 2303, dated October 1983

TM 5-805-4/AFJMAN 32-1090

Paragraph Page Partitions and Enclosures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3 9-1 Mufflers and Duct Lining for Ducted Ventilation System . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4 9-1 Sound Levels for Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5 9-1

CHAPTER 10. NOISE AND VIBRATION MEASUREMENTS

Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 10-1 Sound and Vibration Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2 10-1 Measurement of Noise and Vibration in Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3 10-2 Measurement of Noise and Vibration Outdoors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4 10-2

APPENDIX A. REFERENCES

B. BASICS OF ACOUSTICS

C. SOUND LEVEL DATA FOR MECHANICAL AND ELECTRICAL EQUIPMENT

GLOSSARY

BIBLIOGRAPHY

List of Figures Page

FIGURE 2-1. Noise Criterion (NC) curves 2-2 2-2. Room Criterion (RC) curves 2-3 2-3. Approximate Sensitivity and Response of People to Feelable Vibration 2-6 2-4. Vibration Criteria for Damage Risk to Buildings 2-7 2-5. Vibration Criteria for Sensitive Equipment in Buildings 2-8 2-6. Vibration Acceleration Levels of a Large Vibrating Surface that Will Produce Radiated Sound Levels 2-9

Into a Room Approximating the Sound Levels of the NC Curves 3-1. Approximate Relationship Between Relative Sound Pressure Level (REL SPL) and Distance to a Sound 3-2

Source for Various Room Constant Values 3-2. Room Constant Estimate 3-5 4-1. Improvement in Transmission Loss Caused by Air Space Between Double Walls Compared to Single 4-3

Wall of Equal Total Weight, Assuming no Rigid Ties Between Walls 4-2. Natural Frequency of a Double Wall With an Air Space 4-4 4-3. Schematic Illustration of Flanking Paths of Sound 4-5 4-4. Typical Floating Floor Construction 4-20 4-5. Suggested Applications and Details of Floating Floors for Improvement of Airborne Sound Transmission Loss 4-21 4-6. Structureborne Flanking Paths of Noise (Paths 2 and 3) Limit the Low Sound Levels Otherwise 4-22

Achievable With High-TL Floating Floor Construction (Path 1) 4-7. Nonflat Concrete Floors 4-22 5-1. Inverse Square Law of Sound Propagation 5-2 5-2. Downwind sound diffraction 5-6 5-3. Upwind Sound Diffraction 5-6 5-4. Effects of Temperature Gradients on Sound Propagation 5-7 5-5. Outdoor Sound Propagation Near the Ground 5-7 5-6. Parameters and Geometry of Outdoor Sound Barrier 5-8 5-7. Examples of Surfaces That Can Reflect Sound Around or Over a Barrier Wall 5-10 5-8. Compound Barriers 5-11 5-9. Edge Effects at End of Barrier 5-12

5-10. Elevation Profile of Cooling Tower Used in Example 5-14 7-1. Good and Poor Air Delivery Conditions to Air Outlets 7-4 7-2. Plan View of Supply Duct for Example 7-12 8-1. Suggested Arrangement of Ribbed Neoprene Pads for Providing Resilient Lateral Restraint to a Spring 8-4

Mount 8-2. Schematic of Vibration Isolation Mounting for Fan and Drive-Assembly of Propeller-Type Cooling Tower 8-6 8-3. Schematic of a Resilient Clamping Arrangement With Ribbed Neoprene Pads 8-7 B-1. Approximate Electrical Frequency Response of the A-, B-, and C-Weighted Networks of Sound Level B-7

Meters B-2. Transmissibility of a Simple Undamped Single Degree-of-Freedom System B-1 C-1. Sound Pressure Levels of Reciprocating Compressors at 3-ft. Distance C-2 C-2. Sound Pressure Levels of Centrifugal Compressors at 3-ft. Distance C-3 C-3. Principal Types of Cooling Towers C-6 C-4. Sound Pressure Levels of Pumps at 3-ft. Distance C-li C-5. Sound Pressure Levels of Air Compressors at 3-ft. Distance C-13 C-6. Sound Pressure Levels of TEFC Motors at 3-ft. Distance C-22 C-7. Sound Pressure Levels of DRPR Motors at 3 ft. Distance C-23 C-8. Sound Pressure Levels of Steam Turbines at 3 ft. Distance C-24

List of Tables

Page

Table 2-1. Category Classification and Suggested Noise Criterion Range for Intruding Steady-State Noise as Heard 2-4 in Various Indoor Functional Activity Areas

2-2. Speech Interference Levels (SIL) That Permit Barely Acceptable Speech Intelligibility at the Distances 2-5 and Voice Levels Shown

3-1. Reduction of SPL (in dB) in Going From Normalized 3-ft. Distance and 800-ft.2 Room Constant to Any 3-3 Other Distance and Room Constant

3-2. REL SPL Values for a Range of Distances “D” and Room Constants “R”, for Use With PWL Data 3-4 3-3. Sound Absorption Coefficients of General Building Materials and Furnishings 3-6 3-4. Low Frequency Multipliers For Room Constants 3-7 3-5. Summary of Data and Calculations Illustrating Use of Equation 3-1 3-8 3-6. Summary of Data and Calculations Illustrating Use of Equation 3-2 3-9 4-1. Wall or Floor Correction Term “C” for Use in the Equation NR TL + “C” 4-2 4-2. Transmission Loss (in dB) of Dense Poured Concrete or Solid-Core Concrete Block or Masonry 4-7 4-3. Transmission Loss (in dB) of Hollow-Core Dense Concrete Block or Masonry 4-8 4-4. Transmission Loss (in dB) of Cinder Block or Other Lightweight Porous Block Material with Impervious 4-9

Skin on Both Sides to Seal Pores 4-5. Transmission Loss (in dB) of Dense Plaster 4-10 4-6. Transmission Loss (in dB) of Stud-Type Partitions 4-11 4-7. Transmission Loss (in dB) of Plywood, Lumber, and Simple Wood Doors 4-13 4-8. Transmission Loss (in dB) of Glass Walls or Windows 4-14 4-9. Transmission Loss (in dB) of Typical Double-Glass Windows, Using ¼-in.-Thick Glass Panels With 4-15

Different Air Space Widths 4-10. Transmission Loss (in dB) of a Filled Metal Panel Partition and Several Commercially Available 4-16

Acoustic Doors 4-11. Approximate Transmission Loss (in dB) of Aluminum, Steel and Lead 4-17 4-12. Transmission Loss (in dB) of Type 1 Floor-Ceiling Combinations 4-18 4-13. Transmission Loss (in dB) of Type 2 Floor-Ceiling Combinations 4-18 4-14. Transmission Loss (in dB) of Type 3 Floor-Ceiling Combinations 4-19 4-15. Transmission Loss (in dB) of Type 4 Floor-Ceiling Combinations 4-19 4-16. Approximate Improvement in Transmission Loss (in dB) When Type 5 Floating Floor is Added to Types 4-20

1 through 4 Floor-Ceiling Combinations 5-1. Molecular Absorption Coefficients, dB per 1000 ft., as a Function of Temperature and Relative Humidity 5-3 5-2. Values of Anomalous Excess Attenuation per 1000 ft. 5-4 5-3. Distance Term (DT), in dB, to a Distance of 80 ft. 5-4 5-4. Distance Term (DT), in dB, at Distances of 80 ft. to 8000 ft. 5-5 5-5. Insertion Loss for Sound Transmission Through a Growth of Medium-Dense Woods 5-8 5-6. Insertion Loss of an Ideal Solid Outdoor Barrier 5-9 5-7. Approximate Noise Reduction of Typical Exterior Wall Constructions 5-13 5-8. Location “A” Cooling Tower Problem 5-15 5-9. Location “B” Cooling Tower Problem 5-15 7-1. Plenum/Ceiling Transfer Factor 7-3 7-2. Approximate Natural Attenuation in Unlined Sheet-Metal Ducts 7-5 7-3. Attenuation in Lined Ducts 7-6 7-4. Power Level Loss at Branches 7-7 7-5. End Reflection Loss 7-8 7-6. Losses Caused by Duct Elbows 7-9 7-7. Representative IL Values for Sound Attenuators 7-10 8-1. General Types and Applications of Vibration Isolators 8-2 8-2. Vibration Isolation Mounting for Centrifugal and Axial-Flow Fans 8-8 8-3. Vibration Isolation Mounting for Reciprocating Compressor Refrigeration Equipment Assembly 8-9 8-4. Vibration Isolation Mounting for Rotary Screw Compressor Refrigeration Equipment Assembly 8-12 8-5. Vibration Isolation Mounting for Centrifugal Compressor Refrigeration Equipment Assembly 8-13 8-6. Vibration Isolation Mounting for Absorption-Type Refrigeration Equipment Assembly 8-14 8-7. Vibration Isolation Mounting for Boilers 8-15 8-8. Vibration Isolation Mounting for Propeller-Type Cooling Towers 8-16 8-9. Vibration Isolation Mounting for Centrifugal-Type Cooling Towers 8-17

8-10. Vibration Isolation Mounting for Motor-Pump Assemblies 8-18 8-11. Vibration Isolation Mounting for Steam-Turbine-Driven Rotary Equipment 8-19 8-12. Vibration Isolation Mounting for Transformers 8-20 8-13. Vibration Isolation Mounting for One- or Two-Cylinder Reciprocating-Type Air Compressors in the 10- to 8-21

100-hp Size Range 9-1. Sample Sound Pressure Level Specification 9-3 9-2. Sample Sound Power Level Specification 9-4 B-1. Bandwidth and Geometric Mean Frequency of Standard Octave and 1/3 Octave Bands B-6

List of Tables (Cont**d)

Page Table B-2. Relationship Between Changes in Sound Level, Acoustic Energy Loss, and Approximate Relative B-9

Loudness of a Sound B-3. Suggested Schedule for Estimating Relative Vibration Isolation Effectiveness of a Mounting System B-11 C-1. Sound Pressure Levels (in dE at 3-ft. Distance) for Packaged Chillers with Reciprocating Compressors C-2 C-2. Sound Pressure Levels (in dE at 3-ft. Distance) for Packaged Chillers with Rotary Screw Compressors C-3 C-3. Sound Pressure Levels (in dE at 3-ft. Distance) for Packaged Chillers with Centrifugal Compressors C-4 C-4. Sound Pressure Levels (in dB at 3-ft. Distance) for Absorption Machines C-4 C-5. Sound Pressure Levels (in dE at 3-ft. Distance from the Front) for Boilers C-S C-6. Sound Pressure Levels (in dE at 3-ft. Distance) for High-Pressure Thermally Insulated Steam Valves C-S and Nearby Piping C-7. Frequency Adjustments (in dE) for Propeller-Type Cooling Towers C-7 C-8. Frequency Adjustments (in dE) for Centrifugal-Fan Cooling Towers C-7 C-9. Correction to Average SPLs for Directional Effects of Cooling Towers C-8

C-10. Approximate Close-In SPLs (in dB) Near the Intake and Discharge Openings of Various Cooling Towers C-9 (3- to 5-ft. Distance)

C-11. Overall and A-Weighted Sound Pressure Levels (in dB and dE(A) at 3-ft. Distance) for Pumps C-1 C-12. Frequency Adjustments (in dB) for Pumps C-1 C-13. Specific Sound Power Levels Kw (in dE), Blade Frequency Increments (in dB) and Off-Peak Correction C-12 for Fans of Various Types, for Use in Equation C-S C-14. Approximate Octave-Band Adjustments for Estimating the PWL of Noise Radiated by a Fan Housing C-13 and its Nearby Connected Duct Work C-15. Sound Pressure Levels (in dE at 3-ft. Distance) for Air Compressors C-14 C-16. Correction Terms (in dB) to be Applied to Equation C-6 for Estimating the Overall PWL of the Casing C-14

Noise of a Reciprocating Engine C-17. Frequency Adjustments (in dE) for Casing Noise of Reciprocating Engines C-15 C-18. Frequency Adjustments (in dB) for Turbocharger Air Inlet Noise C-15 C-19. Frequency Adjustments (in dE) for Unmuffled Engine Exhaust Noise C-16 C-20. Overall PWLs of the Principal Noise Components of Gas Turbine Engines having no Noise Control C-17

Treatments C-21. Frequency Adjustments (in dE) for Gas Turbine Engine Noise Sources C-18 C-22. Approximate Noise Reduction of Gas Turbine Engine Casing Enclosures C-19 C-23. Approximate Directivity Effect (in dB) of a Large Exhaust Stack Compared to a Nondirectional Source C-20 of the Same Power C-24. Frequency Adjustments (in dE) for TEFC Electric Motors C-21 C-25. Frequency Adjustments (in dE) for DRPR Electric Motors C-23 C-26. Sound Pressure Levels (in dB at 3 ft distance) for Steam Turbines C-24 C-27. Approximate Sound Pressure Levels (in dE at 3-ft. Distance) for Gears, in the 125-through 8000-Hz C-25

Octave Bands, from Equation C-16 C-28. Approximate Overall PWI (in dE) of Generators, Excluding the Noise of the Driver Unit C-25 C-29. Frequency Adjustments (in dE) for Generators Without Drive Unit C-26 C-30. Octave-Band Corrections (in dE) to be Used in Equation C-17 for obtaining PWL of Transformers in C-27

Different Installation Conditions

CHAPTER 1

GENERAL

1-1. Purpose.

This manual provides qualified designers the crite-ria and guidance required for design and construc-tion of those features related to noise and vibra-tion control of mechanical equipment systems most commonly encountered in military facilities.

1-2. Scope.

These criteria apply to all new construction and to major alteration of existing structures. US mili-tary facilities that require higher standards be-cause of special functions or missions are not covered in this manual; criteria for these and other exceptions are normally contained in a de-sign directive. If standards given in this manual and its referenced documents do not provide all the needs of a project, recognized construction practices and design standards can be used.

1-3. References.

Appendix A contains a list of references used in this manual.

1-4. Noise Estimates.

Noise level estimates have been derived for vari-ous types of mechanical equipment, and in some cases graded for power or speed variations of the noise-producing machines. The noise level esti-mates quoted in the manual are typically a few decibels above the average. Therefore, these noise level estimates should result in noise control de-signs that will adequately “protect” approximately 80 to 90 percent of all equipment. It is unecono-mical to design mechanical equipment spaces to protect against the noise of all the noisiest possible equipment; such overdesign would require thicker and heavier walls and floors than required by most of the equipment. The noise estimates and the noise control designs presented may be used with reasonable confidence for most general pur-poses. Data and recommendations are given for mechanical equipment installations on-grade and in upper-floor locations of steel and concrete build-ings. Though they can also be applied to equip-ment located in upper floors of buildings on all-wood construction, the low mass of such structures for the support of heavy equipment will yield higher noise and vibration levels than would normally be desired. Data and recommendations are also given for the analysis of noise in the surrounding neighborhood caused by mechanical equipment, such as cooling towers. On-site power plants driven by reciprocating and gas turbine engines have specific sound and vibration prob-lems, which are considered separately in the man-ual TM 5-805-9/AFM 88-20.

1-5. English Metric Units.

English units are used throughout this manual for conventional dimensions, such as length, volume, speed, weight, etc. Metric units are used in special applications where the United States has joined with the International Standards Organization (ISO) in defining certain acoustic standards, such as 20 micropascal as the reference base for sound pressure level.

1-6. Explanation of Abbreviations and Terms.

Abbreviations and terms used in this manual are explained in the glossary.

1-1

CHAPTER 2

NOISE AND VIBRATION CRITERIA

2-1. General.

This chapter includes data and discussions on generally acceptable indoor noise and vibration criteria for acceptable living and working environ-ments. These criteria can be used to evaluate the suitability of existing indoor spaces and spaces under design.

2-2. Noise Criteria In Buildings.

Room Criteria (RC) and Noise Criteria (NC) are two widely recognized criteria used in the evalua-tion of the suitability of intrusive mechanical equipment noise into indoor occupied spaces. The Speech Interference Level (SIL) is used to evaluate the adverse effects of noise on speech communica-tion.

a. NC curves. Figure 2-1 presents the NC curves. NC curves have been used to set or evaluate suitable indoor sound levels resulting from the operation of building mechanical equip-ment. These curves give sound pressure levels (SPLs) as a function of the octave frequency bands.

The lowest NC curves define noise levels that are quiet enough for resting and sleeping, while the upper NC curves define rather noisy work areas where even speech communication becomes diffi-cult and restricted. The curves within this total range may be used to set desired noise level goals for almost all normal indoor functional areas.

In a strict interpretation, the sound levels of the mechanical equipment or ventilation system under design should be equal to or be lower than the selected NC target curve in all octave bands in order to meet the design goal. In practice, how-ever, an NC condition may be considered met if the sound levels in no more than one or two octave bands do not exceed the NC curve by more than one or two decibels.

b. Room criterion curves. Figure 2-2 presents the Room Criterion (RC) curves. RC curves, like NC curves, are currently being used to set or evaluate indoor sound levels resulting from the operation of mechanical equipment. The RC curves differ from the NC curves in three important respects. First, the low frequency range has been extended to include the 16 and 31.5 Hz octave bands. Secondly, the high frequency range at 2,000 and 4,000 Hz is significantly less permissive, and the 8,000 Hz octave band has been omitted since most mechanical equipment produces very little noise in this frequency region. And thirdly, the range over which the curves are defined is limited from RC 25 to RC 50 because; 1) applications below RC 25 are special purpose and expert con-sultation should be sought and; 2) spaces above RC 50 indicate little concern for the quality of the background sound and the NC curves become more applicable.

Table 2-1 lists representative applications of the RC curves. The evaluation of the RC curves is different than that for the NC curves. In general the sound levels in the octave bands from 250 to 2,000 Hz are lower than those of the NC curves.

Should the octave band sound levels below 250 Hz be greater than the criteria a potential “rumble” problem is indicated. As a check on the relative rumble potential, the following procedure is recom-mended:

(1) Sum the sound pressure levels in the octave bands from 31.5 through 250 Hz on an energy basis (See app B).

(2) Sum the sound pressure levels in the octave bands from 500 through 4,000 Hz on an energy basis.

(3) Subtract the high frequency sum (step 2) from the low frequency sum (step 1).

(4) If the difference is +30 dB or greater, a positive subjective rating of rumble is expected, if the difference is between +25 and +30 dB a subjective rating of rumble is possible, if the difference is less than +20 dB a subjective rating of rumble is unlikely. Also indicated on the RC curves (fig 2-2) are two regions where low fre-quency sound, with the octave band levels indi-cated, can induce feelable vibration or audible rattling in light weight structures.

c. Speech interference levels. The speech interfer-ence level (SIL) of a noise is the arithmetic average of the SPLs of the noise in the 500-, 1000-, and 2000-Hz octave bands. The approximate condi-tions of speech communication between a speaker and listener can be estimated from table 2-2 when the SIL of the interfering noise is known. Table 2-2 provides “barely acceptable” speech intelligi-bility, which implies that a few words or syllables will not be understood but that the general sense of the discussion will be conveyed or that the listener will ask for a repetition of portions missed.

2-1

Region A: High probability that noise-induced vibration levels in lightweight wall and ceiling constructions will be clearly feelable; anticipate audible rattles in light fixtures, doors, windows, etc.

Region B: Noise-induced vibration levels in lightweight wall and ceiling con-structions may be moderately feelable; slight possibility of rattles in light fix-tures, doors, windows, etc.

Region C: Below threshold of hearing for continuous noise.

Reprinted with permission from The 1987 ASHRAE Handbook, HVAC Systems and Applications

Figure 2-2. Room Criterion (RC) Curves

The quality of telephone usage is related to SIL approximately as follows:

SIL Range (dB) for Telephone Usage 30-45 S a t i s f a c t o r y 45-60 Slightly difficult 60-75 Difficult Above 75 Unsatisfactory

d. Limitations. The indoor noise criteria consid-ered above assume that the noise is almost contin-uous and of a fairly steady nature (not enough modulating or fluctuating up and down in level or frequency to attract attention), and there are no raucous, unpleasant sounds or strongly tonal sounds. If any of these assumptions are not met, 2-3

Table 2-1. Category Classification and Suggested Noise Criterion Range for Intruding Steady-State Noise as Heard in Various Indoor Functional Activity Areas.

Category Area (and Acoustic Requirements) Noise Criteriona

1 Bedrooms, sleeping quarters, hospi- NC-20 tals, residences, apartments, to hotels, motels, etc. (for sleeping, NC-30 resting, relaxing).

2 Auditoriums, theaters, large meeting NC-15 rooms, large conference rooms, radio to studios, churches, chapels, etc. NC-30 (for very good listening conditions).

3 Private offices, small conference NC-30 rooms, classrooms, libraries, etc. to (for good listening conditions). NC-35

4 Large offices, reception areas, NC-35 retail shops and stores, cafeterias, to restaurants, etc. (for fair listening NC-40 conditions).

5 Lobbies, drafting and engineering rooms, laboratory work spaces, main-tenance shops such as for electrical equipment,etc. (for moderately fair listening conditions).

NC-40

to

NC-50

6 Kitchens, laundries, shops, garages, NC-45 machinery spaces, power plant control to rooms, etc. (for minimum acceptable NC-65 speech communication, no risk of hearing damage).

the sound level criteria should be even lower than 2-3. Vibration Criteria In Buildings.

the criteria normally considered applicable. This criteria given above is intended to be illustrative;

any occupied or habitable area not identified in the list can be assigned to one of these categories on the basis of similarity to the types of areas already listed. Generally, where a range of criteria is given, the lower values should be used for the more critical spaces in the category and for non-military areas outside the control of the facility;

the higher of the range of criteria may be used for the less critical spaces in the category. Certain short-term infrequent sounds (such as the weekly testing of a fire pump or an emergency power generator) may be allowed to exceed normal crite-ria in relatively noncritical areas as long as the normal functions of these areas are not seriously restricted by the increase in noise.

2-4

Structural vibration in buildings, which results in feelable vibration, produces structural or superfi-cial damage of building components or interferes with equipment operation is unacceptable. In addi-tion large building components that vibrate can produce unacceptable sound levels.

a. Vibration criteria for occupants. Figure 2-3 shows the approximate occupant response to build-ing vibration levels. An approximation of the “threshold of sensitivity” of individuals to feelable vibration is shown by the shaded area of figure 2-3, labeled “barely perceptible.” Other typical responses of people to vibration are indicated by the other zones in figure 2-3. These reactions or interpretations may vary over a relatively wide range for different individuals and for different ways in which a person might be subjected to

Table 2-2. Speech Interference Levels (SIL) That Permit Barely Acceptable Speech Intelligibility at the Distances and Voice Levels Shown.

Distance (ft.)

1/2

Normal Raised

74 80

68 74

62 68

56 62

53 59

50 56 48 54

46 52 44 50

Voice Level

Very Loud

Shouting

SIL is arithmetic average of noise levels in the 500-, 1000-, and 2000-Hz octave frequency bands. SIL values apply for average male voices (reduce values 5 dR for female voice), with speaker and listener facing each other, using unexpected work material. SIL values may be increased 5 dB when familiar material is spoken. Distances assume no nearby reflecting surface to aid the speech sounds.

vibration (standing, seated, through the finger tips). The lower portion of the “barely perceptible” range is most applicable to commercial installa-tions. Complaints of building vibration in residen-tial situations can arise even if the vibration levels are slightly below the lower portion of the “barely perceptible” range. The choice of a vibra-tion criteria, for annoyance due to feelable vibra-tion, will be determined by the usage of the space and the perceived sensitivity of the occupants.

There should not be a problem with perceptible vibration if the levels are 6 to 8 dB below the “barely perceptible” range of figure 2-3.

b. Vibration Criteria for Building Structures.

High amplitude vibration levels can cause damage to building structures and components. When vi-bration is destructive to building component the vibration will be highly perceptible to the building occupants. A structural vibration velocity of 2.0 in/sec has commonly been used as an upper safe limit for building structures, and vibrations above this value will have adverse environmental im-pact. A vibration velocity of 1.0 in/sec be used as a normally safe vibration upper limit with respect to structural damage. Vibrations with a velocity level greater than 1.0 in/sec should be avoided or special arrangements should be made with the owners of the exposed structure. Even with a vibration level of 1.0 in/sec superficial damage may occur in isolated instances. Superficial damage can consist of small cracking in brittle facades such as plaster.

In order to ensure that the possibility of superfi-cial damage is minimized a vibration criteria of

0.2 in/sec has been recommended. And finally for very old structures an even lower level of 0.05 in/sec is recommended. The manner in which the level is to be determined is a function of the type of vibration expected or experienced. For continu-ous vibration the RMS level should be used. For impulsive vibration the Peak value is to be used.

See appendix B for a discussion of Peak and RMS vibration. On figure 2-4 the vibration limits men-tioned above have been plotted in terms of acceler-ation level in dB re 1 micro G.

c. Vibration Criteria for Sensitive Equipment.

Building vibration may be disturbing to the use or proper operation of vibration-sensitive equipment, such as electron microscopes and other special chemical, medical, or industrial instruments or processes. Figure 2-5 shows vibration criteria for some sensitive equipment types. To achieve these low level vibration levels special building construc-

2-5

Figure 2-3. Approximate Sensitivity and Response of People to Feelable Vibration.

tion, mechanical equipment selection and isola- of acceleration level of a large surface. These tion, and vibration isolation for the sensitive NC-equivalent curves show the vibration accelera-equipment are required. tion levels of a large vibrating surface (such as a

d. Vibration criteria for sound control. Vibrating wall, floor, or ceiling of a room> that will produce building components will produce sound radiation radiated sound having approximately the octave which may be unacceptable. Figure 2-6 shows band sound pressure levels of the NC curves “NC-equivalent” sound level curves as a function (shown earlier in figure 2-1).

2-6

Figure 2-4. Vibration Criteria for Damage Risk to Buildings.

2-7

Note - A - 100 X Microscopes.

B - 500 X Microscopes.

C - 1,000 X Microscopes.

D - Electron Beam Mircoscopes to 0.3 micrometer geometries.

E - Anticipated Adequate for future low submicron geometries.

Figure 2-5. Vibration Criteria for Sensitive Equipment in Buildings.

2-8

Figure 2-6. Vibration Acceleration Levels of a Large Vibrating Surface that Will Produce Radiated Sound Levels Into a Room Approximating the Sound Levels of the NC Curves.

2-9

CHAPTER 3

SOUND DISTRIBUTION INDOORS

3-1. General.

This chapter provides data and procedures for deter-mining sound pressure levels in enclosed rooms due to sources of sound contained within the room.

3-2. Sound Pressure level In A Room.

The sound pressure levels at a given distance or the sound power levels for individual equipment items can often be obtained from equipment sup-pliers. Appendix C also provides sound level and power level estimates for general classes of me-chanical equipment. Once the characteristics of the sound source has been determined, then the sound level at any location within an enclosed space can be estimated. In an outdoor “free field” (no reflecting surfaces except the ground), the sound pressure level (SPL) decreases at a rate of 6 dB for each doubling of distance from the source.

In an indoor situation, however, all the enclosing surfaces of a room confine the sound energy so that they cannot spread out indefinitely and be-come dissipated with distance. As sound waves bounce around within the room, there is a build-up of sound level because the sound energy is “trapped” inside the room and escapes slowly.

a. Effect of distance and absorption. The reduc-tion of sound pressure level indoors, as one moves across the room away from the sound source, is dependent on the surface areas of the room, the amount of sound absorption material on those areas, the distances to those areas, and the dis-tance from the source. All of this is expressed quantitatively by the curves of figure 3-1. Figure 3-1 offers a means of estimating the amount of SPL reduction for a piece of mechanical equipment (or any other type of sound source> in a room, as one moves away from some relatively close-in distance to any other distance in the room, pro-vided the sound absorptive properties of the room (Room Constant) is known. Conversely figure 3-1 also provides a means of estimating the sound reduction in a room, from a given source, if the distance is constant and the amount of absorptive treatment is increased.

b. General application of figure 3-1. Figure 3-1 may be used for estimating SPL change from any given condition of Room Constant and distance to any other wanted condition of Room Constant and distance. This can be expressed by equation 3-1:

where D1 and R1 are the distance (in feet) and Room Constant (in ft.2) values for the measured or known sound pressure level LpD1Rl; D2 and R2 are the distance and Room Constant values for the new set of conditions for which the new sound pressure level LpD2R2 is wanted; and REL SPLDIRl and REL SPLD2R2 (in dB) are read from the ordinate (vertical axis) of figure 3-1 for the specific combinations of D1, R1 and D2, R2. For estimating SPL change when only the Room Constant is changed and there is no change of distance (i.e., the equipment distance remains constant), the same distance value for D1 and D2 is used and the equation is solved. For estimating SPL change when only the distance is changed and there is no change in Room Constant (i.e., the equipment remains in the same room, with no change in absorption), the same value of Room Constant for R1 and R2 is used and the equation is solved. For a complete analysis, the calculations must be carried out for each octave frequency band.

c. Simplified table for SPL correction for dis-tance and room constant. Table 3-1 represents a simplification of figure 3-1 for a special condition of distance and room constant. Much of the collec-tion of equipment sound data in appendix C is given in terms of SPL at a normalized distance of 3 feet and a normalized room constant of approxi-mately 800 ft.2 Table 3-5 permits extrapolation from those normalized 3-foot SPLs to some greater distance for a variety of different Room Constants.

Table 3-1 must not be used in converting sound power level (PWL) data to sound pressure level (see equation 3-2 and table 3-2).

d. SPL in a room when PWL is known. The second major use of figure 3-1 is in determining the SPL in a room when the sound power level of the source is known. Equation 3-2 provides this.

Lp D , R = Lw + REL SPLD,R (eq 3-2) where LpD,R is the SPL to be determined at distance D in the room of Room Constant R, Lw the sound power level of the source (in dB re 10-12W) and REL SPLD,R is read from the ordinate of figure 3-1 for the point of intersection of the D and R values specified. In most uses, the value of REL SPLD,R will be negative, so this amounts to a subtraction function. Hence, the signs must be followed carefully. The calculation is repeated for each octave band.

3-1

EQUIVALENT DISTANCE FROM ACOUSTIC CENTER OF A

NONDIRECTIONAL SOURCE;. ”D” (FT.)

Note: This f igure has been ad justed to take into account large obstac les or large p ieces o f equipment d is tr ibuted about the room.

Therefore, the curves for large va lues o f R do not agree wi th s imi lar textbook curves that tend to ignore such obstac les .

Figure 3-1. Approximate Relationship Between “Relative Sound Pressure Level” (REL SPL) and Distance to a Sound Source for Various “Room Constant” values.

e. Simplified table PWL to SPL. As a conve-nience, table 3-2 presents the REL SPL data of figure 3-1 for a number of distance and Room Constant values. This table is for use only in calculating SPL from PWL; it does not give the difference between two REL SPL values, as is given in table 3-1.

3-3. Room Constant.

a. Calculation of room constant. The room con-stant is a measure of the amount of sound absorp-tion that exists within a room. Most current acoustic textbooks give details of a conventional calculation of the Room Constant for any specific room, when the following facts are known: (1) all the room dimensions, (2) the wall, floor, and ceiling materials, (3) the amount and type of acoustic absorption materials, and (4) the sound

3-2 absorption coefficients of the acoustic- materials at various specified frequencies. The calculation is summarized in equation 3-3:

where R is the Room Constant (or “room absorp-tion” as it is often called), S1 is the total area of all the room surfaces having “sound absorption coeffi-cients” S2 is the total area of all the room surfaces having sound absorption coefficient etc.

The areas S1, . . .Sn are expressed in ft.2, and the sound absorption coefficients are dimensionless.

The resulting Room Constant R is also expressed in ft2 The term “sabin” is used in the literature as a unit of room absorption or Room Constant, where one sabin is the absorption provided by 1 ft2 of material having perfect absorption; i.e., having a value of 1.0. In the manual, 1 ft2 of absorption and 1 sabin are used synonymously.

Table 3-1. Reduction of SPL in (dB) in Going from Normalized 3-ft.. Distance and 800-ft.2 Room Constant to Any Other Distance and Room Constant.

Room Constant Distance "D" (in ft.) from Equipment

"R" (ft.2) 3 5 10 15 20 30 40 60 80

100 -5 -4 -4 -4 -4 -4 -4 -4 -4

200 -3 -2 -1 -1 -1 -1 -1 -1 -1

320 -2 0 0 0 0 0 0 0 0

500 -1 1 2 3 3 3 4 4 4

700 0 2 4 4 5 5 6 6 6

1000 1 3 5 6 7 7 8 0 0

2000 1 4 7 0 9 9 10 10 10

3200 2 5 0 9 10 11 12 12 12

5000 2 6 9 11 12 13 14 14 15

7000 2 6 10 12 13 14 15 15 16

10000 2 7 11 13 14 15 16 17 10

20000 2 7 12 14 16 1 8 19 21 22

Infinite 2 7 13 I 16 19 22 25 20 31

Note: Negative value of reduction means an Increase in sound level.

b. Sound absorption coefficients. For most sur-faces and materials, the sound absorption coeffi-cients vary with frequency; hence the Room Con-stant must be calculated for all frequencies of interest. Even room surfaces that are not normally considered absorptive have small amounts of ab-sorption. Table 5-1 gives the published sound absorption coefficients of typical building materi-als. Usually sound absorption coefficients are not measured in the 31, 63 and 8,000 Hz frequencies.

Where the data at these frequencies are not available use 40% of the value of the 125 Hz for the 31 Hz band, 70% of the 125 Hz value for the 63 Hz band and 80% of the 4,000 value for the 8,000 Hz octave band. Values of sound absorption coefficients for specialized acoustical materials must be obtained from the manufacturer.

c. Estimation of room constant. In the early stages of a design, some of the details of a room may not be finally determined, yet it may be necessary to proceed with certain portions of the design. An approximation of the Room Constant can be made using figure 3-2 and table 3-4. The basic room dimensions are required but it is not necessary to have made all the decisions on side wall, floor, and ceiling materials. This simplifica-tion yields a less accurate estimate than does the more detailed procedure, but it permits rapid estimates of the Room Constant with gross, but nonspecific, changes in room materials and sound absorption applications. Then, when a favored condition is found, detailed calculations can be made with equation 3-1.

d. Use of figure 3-2. Figure 3-2 gives a broad relationship between the volume of a typically shaped room and the Room Constant as a function of the percentage of room area that is covered by sound absorption material. Room area means the total interior surface area of floor, ceiling, and all side walls. The Room Constant values obtained from this chart strictly apply at 1000 Hz, but in this simplified procedure are considered applicable for the 2000- through 8000-Hz bands as well.

e. Use of table 3-3, part A. Sound absorption materials are less effective at low frequency (at and below 500 Hz) than at high frequency (at and

3-3

Table 3-2. REL SPL Values for a Range of Distances "D” and Room Constants "R”, for Use With PWL Data.

Room Constant Distance "D" (in ft.) from Equipment

"R" (ft.2) 3 5 10 15 20 30 40 60 80

100 -3 -4 -4 -4 -4 -4 -4 -4 -4

200 -5 -6 -7 -7 -7 -7 -7 -7 -7

320 -6 -7 -8 -8 -9 -9 -9 -9 -9

500 -7 -9 -10 -11 -11 -11 -11 -11 -11

700 -8 -10 -12 -12 -12 -13 -13 -13 -13

1000 -8 -11 -13 -13 -14 -14 -15 -15 -15

2000 -9 -12 -15 -16 -17 -17 -17 -18 -18

3200 -10 -13 -16 -17 -18 -19 -19 -20 -20

5000 -10 -14 -17 -18 -20 -21 -21 -22 -23

7000 -10 -14 -16 -19 -21 -22 -23 -24 -25

10000 -10 -14 -19 -21 -22 -23 -24 -25 -26

20000 -10 -15 -20 -22 -24 -26 -27 -30 -30

Infinite -10 -15 -21 -24 -27 -30 -33 -36 -39 above 1000 Hz). Therefore, the high-frequency Room Constant obtained from figure 3-2 must be reduced to apply to the lower frequencies. Part A of table 3-3 gives a multiplier for doing this. This multiplier is a function of frequency, Noise Reduc-tion Coefficient (NRC) range of any special sound absorption material, and the mounting type for installing the absorption material. The Noise Re-duction Coefficient is the arithmetic average of the sound absorption coefficient at 250, 500, 1,000 and 2,000 Hz. Mounting type A consists of application sound absorptive material applied directly onto a hard backing such as a wall or ceiling. Mounting type B consists of sound absorptive material me-chanically supported with a large air space behind the material, such as a typical suspended ceiling.

f. Use of Table 3-3, part B. Relatively thin wall materials (such as gypsum board, plaster, ply-wood, and glass), even though not normally con-sidered as soft, porous, and absorptive, actually have relatively large values of sound absorption coefficient at low frequency. This is because these thin surfaces are lightweight and are easily driven by airborne sound waves. For this reason they appear as effective sound absorbers at low frequency, and this characteristic should be taken into account in the calculation or estimation of

3-4

Room Constant. Part B of table 3-3 gives a multiplier for doing this.

3-4. Sample Calculations.

Two sample calculations are provided, one in which…